1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device. More particularly, the present invention relates to a method for forming a via hole.
2. Description of the Related Art
As the integration density of semiconductor devices increases, more circuit elements must to be packed in a unit surface area of the device substrate, and circuit elements such as interconnects are necessarily increased between MOS transistors of the IC device, especially semiconductor products such as microprocessor. In many highly integrated semiconductor devices, more than two levels of interconnecting metal layers are demanded, called multilevel interconnects. Between these multiple metal layers, electrically insulating material known as inter-metal dielectrics are used to provide isolation between the metal layers. Vias are formed in these inter-metal dielectric layers that can be filled with electrically conductive material to form plugs that provide electrical connection between the interconnects for different metal layers.
FIGS. 1A through 1D are schematic, cross-sectional views showing the progression of conventional manufacturing steps for a via hole. Referring to FIG. 1A, a substrate 100 having a MOS device is provided, and a metallic layer 102 is formed on the substrate 100. An intermetal dielectric layer 104 (IMD) is deposited conformal to the substrate 100, and a patterned photoresist 106 is formed on the intermetal dielectric layer 104.
As shown in FIG. 1B, the photoresist 106 is used as a mask, then the intermetal dielectric layer 104, which is not covered by the photoresist 106 is removed to expose the metallic layer 102, so that an opening 110 is formed. A polymer layer 108 is unavoidably formed on the surface of the opening 110.
As shown in FIG. 1C, the photoresist 106 is removed.
Referring to FIG. 1D, the polymer layer 108 on the surface of the opening 110 is removed by a solvent including ammonia (NH.sub.4 OH), and a residual polymer layer 109 on the surface of the opening 110 is removed by de-ionized water.
In order to remove the polymer layer 108 on the surface of the opening 110, the solvent including ammonia used, but the ammonia easily reacts with the intermetal dielectric layer 104 along the sidewalls of the opening 110 and the metallic layer 102 at the bottom of the opening 110 to result in a hydroxyl (--OH) group having polarity generated on the surface of the opening 110. Because the hydroxyl group having polarity causes a vapor absorption phenomenon, water evaporates to form air bubbles in the metal via while metal is filled into the metal via hole at a high temperature. A poisoned metal via hole is therefore induced by the vapor absorption phenomenon, which causes poor contact between metals and reduces the device yield. If de-ionized water is used to remove the polymers on the surface of the opening 110, the de-ionized water cannot absolutely eliminate the polymers on the metal via hole further to result in reduced device yield. In addition, a low-conductivity material is generally selected for intermetal dielectric layer 104 to ensure good insulation. Due to the inclusion of ammonia in the solvent used for removing the polymer layer 108 on the surface of the opening 110, a poisoned metal via hole easily occurs in an unlanded metal via process, which uses low conductivity material as an intermetal dielectric layer.